1. Field of the Invention
The invention relates to a method for the manufacture of pig iron in a shaft furnace, more particularly a blast furnace, wherein a taphole of the shaft furnace is opened and pig iron is tapped off from the shaft furnace via the opened taphole, and thereafter the taphole is sealed off by placing plugging compound in the taphole. Such a method is known from the practice of making pig iron in a blast furnace. It is also known to use two tapholes which are operated alternately so that at any time only one taphole is opened for tapping off pig iron from the shaft furnace.
2. Description of the Prior Art
Various methods are used for opening the taphole. One known method is to make a hole in the furnace wall using a drill, which is no easy matter, among other reasons because of the length of the taphole to be made (approximately 2 to 3 meters), and the characteristics of the material of the furnace wall. A particular disadvantage of this method is that the wall of the drilled taphole is not smooth, with the result that the flow front of the pig iron flowing out of the blast furnace via the opened taphole is inhomogeneous. This means that in addition to the primary iron flow (the main flow), so-called secondary flows occur, whereby so-called "sprays" result. The said secondary flows are characterized by a seriously reduced out-flow speed compared with the primary flow. These secondary flows tend to solidify a short distance after leaving the shaft furnace. These solidified secondary flows make it difficult to re-seal the taphole after tapping off because they solidify at least in part in front of the taphole and there form a partial blockage. Moreover, these solidified secondary flows are difficult to remove, which represents a disadvantage for the working conditions of the operating personnel.
An alternative method to this is used in which as soon as tapping off via the taphole is finished, a soft yet hardening plugging compound is placed in the taphole, into which plugging compound a knock rod is then knocked in. The taphole is then opened at the next tapping simply by pulling the rod out again. This method is described for example in JP-A-58-39711 (1983). Compared with the drilling method for opening the taphole, this method has the advantage that it is relatively fast and produces more smoothly finished taphole. However, the method does present the problem that the knock rod has to be knocked into the taphole during a very brief period of time, shortly after the taphole is plugged with the plugging compound, because the plugging compound starts to harden after only a few minutes and in some spots very quickly. As soon as the plugging compound has hardened, or at least has become harder, the problem during knocking in of the knock rod is that the surroundings of the taphole become damaged because the rod and the plugging compound located in front of the rod sticks in the taphole. An additional disadvantage of this method is that, as the plugging compound hardens, it becomes very hard to knock in the rod, and sometimes it can only be knocked into the taphole to a limited extent.
Another method of taphole sealing and reopening involving insertion of a metal rod is shown in JP-A-63-7308 (1988). The rod is inserted together with a ceramic sleeve. The rod is melted, in order to open the taphole. JP-A-58-1007 (1983) describes driving of a ceramic tube into the soft plugging material. The tube is packed and sealed. The tube defines the next taphole. FR-A-2630130 also proposes insertion of a ceramic tube.